Humans program computers. There's a reason standards like MISRA C exist: it is critical to minimize error in human abstractions (code) which run on systems that put people's safety in jeopardy. Humans aren't wired to emulate machines perfectly in their minds, yet computers will do exactly what we tell them to do. You are implicitly placing trust in the humans who programmed those computers.
We saw how human factors can complicate the correctness of code in the Toyota unintended acceleration case. The instruction fed to the system by its programmers were incorrect and not up to industry standards. Computers caused the accidents in that case, despite human intervention by drivers.
And I said I trust a computer more, not that the presence of a computer is automatically enough.
I'm not getting in a manually-controlled plane that's flying centimeters from a hard surface. I will get in some computer-controlled planes doing the same.
(At the very least I want a real-time OS and dedicated range sensors. And the confidence of a plane owner who would lose millions of dollars if anything went wrong.)
There are crop dusters that fly close to the ground and obstacles - do you want to get in a manual one or can I code up a computer controlled one and put you in it?
What you really mean is you want to see safety data and a track record.
As for the actual planes and auto-pilots, the real point is the kinds of engagements and disengagements that work in the air don't necessarily work on the ground and being so close to potential collisions is part of that.
The implication of the hard barrier is that it's not safe to crash into it. If there are big wheels on enormous shock absorbers making it safe to hit the barrier, then a lot less precision is needed, and you can put almost anything in control, even a heavy clamp that keeps the controls skewed slightly toward the barrier. But that's not the scenario anyone else is talking about.